You sound like me - lean with high metabolism and find it hard to put on size! The key really is to eat whenever you can - literally, when you think about it - eat! I take 1 protein shake a day, plus a couple of BCAA caps.If you're waiting that long between meals (6hrs!), but can have a drink, take a meal replacement drink which has protein + carbs in, which you'll need to remain in a catabolic state!
As for routine - the one I'm on at the mo, and is pretty much a common split is:
Day 1 - Chest/ Tris
Day 2 - Rest
Day 3 - Back/Bis
Day 4 - Rest
Day 5 - Legs/Shoulders
Day 6 - Rest
Day 7 - Rest or repeat programme
As for the exercises, you'll have to experiment a little bit both in what ones to do and how to do them to see what works for you, but to start I'd aim for reps in the 6 - 8 range for your main set and use these tried and tested exercises:
Chest: Incline b/bell bench press, Flat d/bell press, cable crossovers
Tris: Close grip-bench press, French press, Cable pressdown
Back: Wide grip chins (or pulldowns), Barbell bent over row, Close grip pulldowns
Bis: EZ B/bell curls, alternate d/bell curls, concentration curls
Legs: Squat, Leg Press, Lunges, Stiff leg deadlift, leg curl, leg extension
Shoulders: D/bell overhead press, Side lateral raises, Bent over lateral raises, shrugs
See which of those work and choose 3 - 4 exercises for the bigger muscle groups and 2 - 3 for thesmaller ones and stick with them. Aim to put on a little bit of weight to the bar or do one more rep (still in your target range) every time you hit the gym, and you will get bigger. And before your main set do 1 - 2 warm up sets using about 70% of your main set weight.
As with it all, it's trial and error as to what will work for you.
Ab work - crunches and leg raises to hit the upper and lower abs respectively once or twice a week! If you're lean like me it doesn't take much to keep this area in shape!
As far as supplements go. Stick with your protein and weight gain shakes to increase your calorie and protein intake. Maybe try cycling Creatine aswell! It's all I've ever used and a good base for someone who wants to stay natural!
Good luck, and let me know how you get on! | 
